Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

651
FXUS63 KLOT 170250
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
950 PM CDT Tue Jun 16 2026

.KEY MESSAGES...

- A dangerous severe weather outbreak, including the potential
  for long tracked, strong-violent tornadoes, is possible
  Wednesday, especially south of I-80.

- Periods of torrential rainfall Wednesday could result in areas
  of flash flooding (some locally significant) and potentially
  some rapid onset river flooding.

&&

.UPDATE...
Issued at 950 PM CDT Tue Jun 16 2026

The forecast appears to be largely on track through Wednesday,
with no changes planned with the evening update. The new 00Z
HRRR has rolled in and certainly remains very concerning for
significant severe weather and heavy rainfall potential across
our area Wednesday afternoon. The main uncertainty continues to
revolve been how far northward into our area the warm front will
reach in the afternoon just ahead of a quickly approaching cold
front. This is particularly the case given that waves of
showers and thunderstorms during the mid to late morning hours
may hold the warm front south across central IL into the early
afternoon. However, in spite of this, a strong southern mass
response is expected to occur just in advance of the very
dynamic ~990 mb low shifting into WI. Accordingly, it remains
quiet feasible that the warm front will still be forced to surge
northward in the afternoon, potentially as far north as around
the I-88/I-290 corridor by mid to late afternoon. This thus adds
increasing concern for the potential for damaging wind gusts in
excess of 75 mph and tornadoes into the Chicago metro area,
particularly in the 2-6 pm timeframe.

In addition to the notable severe weather threat, we also
continue to be concerned with the threat of flash flooding due
to heavy rain rates of 1-2" per hour expected with these storms
in the afternoon. Individual storm speeds are expected to be
quiet fast, owing to the strong kinematics. However, the
potential for a period of training storms could easily result in
localized amounts of 2 to 4 inches and flash flooding. We opted
to hold off on a Flash Flood Watch this evening, but cannot
rule out the need for one with future forecast updates.

KJB

&&

.DISCUSSION...
Issued at 237 PM CDT Tue Jun 16 2026

Tonight:

This is the calm before the proverbial storm as winds quickly
diminish with sunset. Expect temporary mostly clear skies before
mid and high level cloud cover overspreads the region in
advance of Wednesday`s powerful storm system. While the
instability axis will remain off to our west through daybreak,
some isolated to scattered showers may move across portions of
northern and central Illinois between about 4 AM and 7 AM.

Wednesday:

Synoptically, the ingredients appear likely to come together for
a potentially dangerous severe weather outbreak somewhere over
the broader region (favoring I-80 and south). This includes
potentially long tracked intense tornadoes and destructive
straight line wind gusts (and line embedded tornadoes).

Meteorological Setup:

An early-spring like (vs. mid June in actuality) mid and upper
level pattern in place across northern North America features
exceptionally strong west-northwesterly flow aloft around an
unseasonably deep closed low southwest of Hudson Bay. A potent
neutrally tilted short-wave trough and associated intense upper
level jet streak will eject southeastward and result in near
record strong surface cyclogenesis (upper 980s to low 990s mb
surface low) over Minnesota into Wisconsin by early Wednesday
afternoon.

Impressively strong warm and moist advection atop a lingering
stable boundary layer and a rapid increase in large scale
forcing will quickly join forces Wednesday morning. The likely
result will be an area of convection propagating east-southeast
across the area through early afternoon (more on the potential
severe threat with this initial round to follow).

The effective warm front will likely be suppressed south to an
extent in the wake of the morning/early afternoon convection.
However, intense mass response and development of a secondary
surface low will likely result in the sharpening warm front
shifting north during the afternoon. Exactly how far north the
front gets is the million dollar question, so to speak, for the
looming more concerning mid afternoon through early evening
severe threat (discussed below). Regardless of the exact
position of the front, much of if not the entire area is fair
game for waves of intense convection. The system cold front will
sweep across the area between about 7pm and 9pm, quickly
bringing the severe weather threat to an end.

Severe Threat Details:

Round 1 (~8 AM to 1 PM CDT): Initial development of strong to
severe storms over eastern Iowa tomorrow morning should
translate into portions of northern and central Illinois in
tandem with a 60+ kt southwesterly low-level jet by late morning
into early afternoon. Strong effective shear and up to 1-2k
J/kg of MUCAPE could in turn support elevated supercells and a
corresponding threat for damaging to locally destructive winds
and hail. The pattern with this initial round of convection will
be one to watch for gravity wave associated convection, which
would potentially up the ante for the damaging wind threat,
despite little/no surface-based instability.

Our thinking hasn`t changed much with this initial round, with
respect to western and southern/southwestern CWA locales being
most favored for severe weather from "round 1". This certainly
doesn`t preclude the threat extending farther north. There still
could be isolated strong storms with heavy downpours and hails
extending into the Rockford and Chicago metros even if the more
intense convection passes over our southwestern 1/2 (or just
south of that). Finally, we would be remiss to not mention the
possibility of strong wake low winds on the back side of the
initial convection.

Round 2 (2 PM to 9 PM CDT): Presently unknown and unknowable
mesoscale details can be expected to play a notable role in
modulating the locations/corridors of the highest severe threat,
and possibly the magnitude as well (at least within our CWA).
From our assessment, SPC`s depicted level 4 of 5 threat
(moderate risk) area on the updated day 2 outlook continues to
best highlight the most likely areas to have a dangerous severe
weather outbreak. This is tied to where an overlap of incredibly
strong low level (40-50+ kt) and deep layer (70+ kt) shear and
moderately strong instability is most favored to occur.

As already alluded to earlier, the million dollar question is
how far north the sharp warm front is able to push in the wake
of the initial MCS. Lingering cold pool influences are typically
not handled all that well by high-res guidance. In addition, and
on the other hand, we`ll quite literally be in uncharted
territory regarding the expected mass response (recovery back
northward of a volatile parameter space) given the extreme
kinematics at play. The range of depictions in the 12z guidance
suite suggests the reasonable error bar to be between roughly
the US-24 corridor to as far north as near or even just north of
I-80. Thus, a key takeaway here is to absolutely not let one`s
guard down, lest the warm sector push farther north than expected.
Anywhere from near/south of I-88 down to the aforementioned
US-24 corridor is fair game, albeit generally favoring south of
I-80 within the level 4 of 5 threat area.

To the south of the sharp warm frontal boundary (near/south of
the path of the secondary surface low), the progged environment
is akin to those found in winter and early spring severe
weather outbreaks in the southeast US. Discrete or semi-discrete
supercells in such an environment, characterized by 500+ m2/s2
of effective inflow layer SRH and extremely long and looped
hodographs, present a ceiling of long tracked strong to violent
tornadoes. However, with that said, it`s unclear if the storm
mode within our area will lend itself to long tracked and/or
cyclic mesocyclones and tornadoes, or be on the messier/mixed
mode side due to the extremely strong forcing.

In addition, depending on how the boundary layer evolves on the
mesoscale in the wake of the initial MCS, it`s not uncommon to
have a south to north gradient from exceptionally favorable
low-level lapse rates and instability for tornadoes to less
favorable but still sufficient ingredients right near the
northern warm front terminus. Should such a scenario unfold,
this may be a path to modulate/limit the event ceiling tornado
intensity wise, but this is absolutely not something to bank on
in the highest threat areas.

Along with the supercell tornado threat in the system warm
sector, a fast moving line of severe thunderstorms (potential
derecho) may materialize just ahead of the cold front. As we saw
last Thursday, widespread potentially significant wind damage
as well as (potentially strong) line embedded tornadoes are
common in the most intense QLCSs. Considering that effective
shear will be more extreme than Thursday, the above scenario is
certainly on the table for parts of the area. Finally, north of
the sharpening warm front, intense warm and moist advection will
quickly replenish MUCAPE reservoir and could yield scattered
elevated severe storms (hail and wind).

Flash Flooding Threat:

Owing to the cool season-like synoptic setup, rapid poleward
transport of 2"+ PWATs from the 60+ kt low-level jet will "prime
the pump" for torrential to locally excessive rainfall (2"+/hour
rainfall rates). Given the wet antecedent conditions and
elevated river and stream levels across the area, it will take
less rain, even in rural areas, to become problematic. For urban
and highly developed suburban areas, the wet antecedent
conditions would only serve to exacerbate the issues even coming
out of dry patterns. In collaboration with WPC, a rare flash
flood threat level 3 of 4 (moderate risk ERO) has been issued
for Wednesday.

Repeated rounds of storms, if not true backbuilding/training,
particularly near and north of the front, meet aspects of a
Maddox archetype. With 24-hour HREF LPMM QPF pushing 3-4" in
swaths, the level 3 of 4 flood threat appears more than
reasonable. Concern would be urban flooding potentially on the
level of mid May 2020 if conditions come together just wrong
in/near Rockford, Chicago, and flashy river/stream basins in
the nearby Chicago suburbs. Expect a Flood Watch to be issued by
the overnight shift, informed by further guidance and
observational assessment.

Final Takeaway Message:

Given the severe weather parameters in play tomorrow, as well
as the threat for potentially significant flash flooding (even
outside of the higher severe threat areas), it is important to
continue to monitor later forecast updates closely. Review (and
practice) severe weather safety plans. Have multiple redundant
means to receive warning information, and keep mobile devices
charged in the event of power outages.

Castro/Izzi

Wednesday Night Onward:

We should see a break in the active pattern for the rest of the
work week. There are indications that we could get into a more
active northwest flow type pattern heading into the weekend and
beyond. This may include a threat for another strong moisture
laden system and an associated severe weather and flooding
threat on Sunday PM/Father`s Day. In other words, our break may
be short-lived, unfortunately.

Izzi/Castro

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 700 PM CDT Tue Jun 16 2026

Key Messages:

- Abating westerly winds with sunset this evening.

- Active weather day expected on Wednesday, with several waves
  of showers and thunderstorms. The most substantial storms
  (with a severe and very heavy rain threat) are expected in the
  afternoon.

- Wind forecast could become "messy" for a period Wednesday
  afternoon due to effects for the storms and the proximately of
  a surface warm front to the Chicago area terminals.

- Low CIGs and VSBYs (IFR to LIFR) likely to accompany the heavy
  rain producing showers and thunderstorms Wednesday afternoon.

A very impressive and dynamic weather system will track into
the western Great Lakes Wednesday. This promises to produce a
significant severe weather outbreak Wednesday afternoon,
particularly near and south of a surface warm front. This
surface warm front is likely to remain south of the terminals
for much of the day as waves of showers and thunderstorms move
across northern IL. Accordingly, winds across the Chicago area
terminals should largely favor an east-southeasterly direction,
which continues to be highlighted in the TAFs. However, wind
directions could become tricky, and possibly even differ
significantly between say MDW and ORD for a period mid to late
afternoon as the surface warm front attempts to surge northward
just ahead of an incoming surface cold front. There is thus a
play in which the winds at some of the Chicago area terminals
turn south-southwesterly for a short (1-2 hour) period late in
the day before turning westerly with the cold frontal passage by
early evening.

VFR showers should onset across the area terminals by mid
morning on Wednesday (14-15Z). This initial precipitation looks
to be void of lightning and primarily accompanied by VFR
conditions, particularly across northeastern IL, where the low-
level airmass will still be rather dry and stable. This will
change quickly later in the morning, however, as Gulf moisture
quickly surges northward in advance of the approaching weather
system. Therefore, a quick uptick in thunderstorms is expected
across the area terminals after 16Z. Thereafter, periods of
very heavy rain are expected at times through the afternoon,
with IFR to LIFR CIGs and VSBYs likely accompanying this
activity. Some storms will also become severe, with the main
threat being damaging wind gusts in excess of 70 mph. A notable
tornado threat will also exist, especially south of the Chicago
terminals in the afternoon.

Conditions will begin to improve into early Wednesday evening
(00-01Z), as westerly winds set up in the wake of the cold
frontal passage.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement from Wednesday afternoon through
     Thursday morning for ILZ006-ILZ103-ILZ104.

IN...None.
LM...Small Craft Advisory until 9 PM CDT this evening for the IL
     and IN nearshore waters.

&&

$$

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